In order to cable terminal portions in buildings, such as apartment blocks or offices or houses, and in order to serve such buildings with additional cables such as optical fiber cables, telephone cables, electric cables, and TV cables, telecommunications network operators make use, wherever possible, of existing tubular infrastructure, comprising various cable ducts already present in buildings.
Such cable ducts are present in most rooms in buildings and they are used mainly for telephone cabling, electric cabling, or cabling for cable TV. The paths they follow vary considerably as a function of the type of building.
Reusing such cable ducts avoids laying additional cables where they are visible, where such a solution often requires the collective approval of a condominium, which is often difficult to obtain. The use of cable ducts also guarantees that the installation will be long-lasting, since cables are protected against impacts and other alteration work of wall surfaces.
It is therefore advantageous to reuse existing cable ducts as often as possible, even if they are already occupied, with this also being beneficial in terms of how quickly cables can be laid, and thus of cost.
Nevertheless, this is not always possible, either because the existing cable duct does not have enough room, or because the building does not have any such cable ducts (as in old buildings, for example).
While a cable is being laid in a cable duct, cable installation requires traction to be applied to the cable. Traction on the cable may be combined with applying thrust to the cable in order to limit traction forces.
In general, the cables used nowadays for cabling networks in buildings are generally flexible or even very flexible. That constitutes an advantage when a cable is being laid where it is visible, for example, a cable can then be fitted more closely around corners of walls, door frames, baseboards, . . . , but that reduces the effectiveness with which a cable can be passed along a duct.
The optical cables that are presently available on the market have very low force limits. For example, a cable having a diameter of 3 millimeters (mm) can withstand a force of 15 decanewtons (daN) to 20 daN, and a 4 mm cable can withstand about 40 daN.
Those force limits are such that an agent installing the cable and pulling it by hand can rapidly reach and exceed those limits, thereby damaging or even breaking the fiber under certain conditions of cable bending.
Pulling a cable along a duct that is readily occupied by other cables increases those risks.
It is not possible to envisage creating intermediate assistance points along a duct since that would require walls to be pierced, giving rise to delays and extra costs.
The installer must therefore take special precautions when installing such cables. These precautions are not compatible with economic imperatives of passing a cable in a minimum amount of time.